1. Field of the Invention
The present invention relates to an edge reflection type surface acoustic wave device which utilizes an SH (shear horizontal) type surface acoustic wave.
2. Description of the Related Art
Edge reflection type surface acoustic wave devices which utilize an SH-type surface acoustic wave are well known. The SH-type surface acoustic wave refers to surface acoustic waves such as a EGS (Bleustein-Gulyaev-Shimizu) wave or a Love wave which have a displacement that is perpendicular to the direction of propagation of the surface acoustic wave and include a main component which is parallel to the surface of the substrate. Of these edge reflection type surface acoustic wave devices, in order to suppress bulk waves or to allow for easy production, some have structures in which a step is provided at the edge of the substrate or a groove is provided on the substrate, and the upper portion of the substrate edge or the inside surface of the groove defines the reflection edge, (refer to Japanese Unexamined Patent Application Publication No. 4-82315 and No. 7-263998). In Japanese Unexamined Patent Application No. 4-82315, for example, it is explained that influences of the bulk wave resonance on the SH wave resonance can be prevented and unwanted spurious responses caused by bulk wave resonance can be efficiently suppressed by providing, at the substrate edge, a step having a greater vertical dimension than the surface of the substrate such that the step is spaced away from the substrate surface resulting in at least 80% of the SH wave energy being concentrated at the step.
However, even if the vertical dimension of the reflection edge is greater than the predetermined value as described above, in some cases, desired resonance characteristics or pass-band characteristics could not be obtained. That is, in a conventional surface acoustic wave device having a reflection edge that is a step or a groove as described above, even if the height of the reflection edge is set to a suitable value, there has been a problem that when the distance between the substrate edge and the reflection edge was larger, ripples occurred in the pass-bands. Moreover, there has been a problem that ripples also occurred as the vertical dimension of the reflection edge became larger.
In order to overcome the problems described above, preferred embodiments of the present invention provide a surface acoustic wave device in which desired resonance characteristics and pass-band characteristics are reliably obtained by reducing the ripples caused by bulk waves.
According to a preferred embodiment of the present invention, a surface acoustic wave device includes a piezoelectric substrate having a pair of substrate edges and an upper surface therebetween. The piezoelectric substrate has at least one inner edge arranged to contact the main region and extending from the upper surface toward a bottom surface of the piezoelectric substrate inside one of the substrate edges. An interdigital transducer is provided on the main region of the piezoelectric substrate such that a SH type surface acoustic wave excited by the interdigital transducer and having a wavelength of xcex are reflected by the at least one inner edge. A distance L between the at least one inner edge and the corresponding one of the substrate edges is preferably substantially equal to about 8xcex or less.
It is preferable that the at least one inner edge has a height H in the range of about 2xcex to about 6xcex.
The surface acoustic wave device is constructed and function to be included in a communication device.
As explained above, in the surface acoustic wave device according to various preferred embodiments of the present invention, by setting the distance between the substrate end-surface and the reflection end-surface to less than about 8xcex, ripples in the pass-band caused by bulk waves are minimized, and excellent resonance characteristics and pass-band characteristics are obtained. Furthermore, by setting the height of the reflection edge within the range of about 2xcex to about 6xcex, ripples in the pass-band are minimized, and excellent resonance characteristics and pass-band characteristics are obtained.
Moreover, by mounting the surface acoustic wave device in a communication device according to another preferred embodiment of the present invention, a communication device with excellent characteristics can be obtained.